#1397 StringToString should ignore method references

pmd-java/src/main/java/net/sourceforge/pmd/lang/java/rule/strings/StringToStringRule.java

@@ -3,12 +3,15 @@
  */
 package net.sourceforge.pmd.lang.java.rule.strings;
 
+import net.sourceforge.pmd.lang.java.ast.ASTMethodReference;
 import net.sourceforge.pmd.lang.java.ast.ASTName;
 import net.sourceforge.pmd.lang.java.ast.ASTVariableDeclaratorId;
+import net.sourceforge.pmd.lang.java.ast.AbstractJavaNode;
 import net.sourceforge.pmd.lang.java.rule.AbstractJavaRule;
 import net.sourceforge.pmd.lang.java.symboltable.JavaNameOccurrence;
 import net.sourceforge.pmd.lang.java.typeresolution.TypeHelper;
 import net.sourceforge.pmd.lang.symboltable.NameOccurrence;
+import net.sourceforge.pmd.lang.symboltable.ScopedNode;
 
 public class StringToStringRule extends AbstractJavaRule {
 
@@ -21,13 +24,26 @@ public class StringToStringRule extends AbstractJavaRule {
             JavaNameOccurrence jocc = (JavaNameOccurrence)occ;
             NameOccurrence qualifier = jocc.getNameForWhichThisIsAQualifier();
             if (qualifier != null) {
-                if (!isArray && qualifier.getImage().indexOf("toString") != -1) {
+                if (!isArray && isNotAMethodReference(qualifier) && qualifier.getImage().indexOf("toString") != -1) {
                     addViolation(data, jocc.getLocation());
-                } else if (isArray && qualifier.getLocation() != null && !(qualifier.getLocation() instanceof ASTName) && qualifier.getImage().equals("toString")) {
+                } else if (isArray && isNotAName(qualifier) && qualifier.getImage().equals("toString")) {
                     addViolation(data, jocc.getLocation());
                 }
             }
         }
         return data;
     }
+
+    private boolean isNotAMethodReference(NameOccurrence qualifier) {
+        return isNotA(qualifier, ASTMethodReference.class);
+    }
+
+    private boolean isNotAName(NameOccurrence qualifier) {
+        return isNotA(qualifier, ASTName.class);
+    }
+
+    private boolean isNotA(NameOccurrence qualifier, Class<? extends AbstractJavaNode> type) {
+        ScopedNode location = qualifier.getLocation();
+        return location == null || !(type.isAssignableFrom(location.getClass()));
+    }
 }

pmd-java/src/test/resources/net/sourceforge/pmd/lang/java/rule/strings/xml/StringToString.xml

@@ -129,6 +129,20 @@ public class Foo {
         MyObject o = new MyObject(); //MyObject has no relation with String
         System.out.println(Foo.toString(o)); //PMD violation false positive
     }
+}
+        ]]></code>
+    </test-code>
+    <test-code>
+        <description>#1397 StringToString should ignore method references</description>
+        <expected-problems>0</expected-problems>
+        <code><![CDATA[
+public class Foo {
+    private void log(Supplier<String> msg) { }
+    public void run() {
+        String abc = "abc";
+        log(abc::toString); // fails rule
+        log(() -> abc); // passes rule
+    }
 }
         ]]></code>
     </test-code>

src/site/markdown/overview/changelog.md

@@ -15,6 +15,7 @@
 *   [#1370](https://sourceforge.net/p/pmd/bugs/1370/): ConsecutiveAppendsShouldReuse not detected properly on StringBuffer
 *   [#1371](https://sourceforge.net/p/pmd/bugs/1371/): InsufficientStringBufferDeclaration not detected properly on StringBuffer
 *   [#1384](https://sourceforge.net/p/pmd/bugs/1384/): NullPointerException in ConsecutiveLiteralAppendsRule
+*   [#1397](https://sourceforge.net/p/pmd/bugs/1397/): StringToString should ignore method references
 *   [#1398](https://sourceforge.net/p/pmd/bugs/1398/): False positive for GuardLogStatementJavaUtil with Log4j
 *   [#1399](https://sourceforge.net/p/pmd/bugs/1399/): False positive for VariableNamingConventions with annotation @interface
 *   [#1400](https://sourceforge.net/p/pmd/bugs/1400/): False positive with JUnit4TestShouldUseBeforeAnnotation